Because of the recent advances in the successful correction of renovascular hypertension (RVHT), a more effective screening procedure for renovascular disease is needed. A number of nuclear medicine studies have been proposed for this purpose but no single procedure has been judged to be satisfactory in terms of sensitivity and specificity. Preliminary investigations at our institution have indicated that computer analysis of first pass studies of a 9-9mTc-DTPA bolus through the renovascular bed can provide important information on renal perfusion in patients with hypertension. Several parameters of the DTPA time-activity curves have been shown to correlate with angiographically documented renal artery stenosis (RAS). Further investigations in a canine model of 2 kidney, 1 clip Goldblatt hypertension have resulted in correlations between several parameters of the 90 second renal flow curves and physiological measurements of renal plasma flow and glomerular filtration rate (GFR). More recently, we have combined our DTPA studies with parenteral converting enzyme inhibition (CEI). Preliminary data from this combined technique in our canine model have yielded some striking observations. CEI in animals with unilateral renal artery stenosis results in a significant alteration in the shape of the DTPA renal flow curves with a concomitant fall in the GFR of the stenotic kidney. This observation is consistent with the hypothesis that angiotensin II plays a crucial role in maintaining GFR by mediating efferent arteriolar resistance. A limited number of observatiosn by us and by others suggest that this phenomenon occurs in patients with RVHT who are administered oral CEI prior to nuclear studies. It is proposed that we apply our computer-assisted DTPA renal flow studies with CEI to both the experimental dog model of RAS and the human form of RVHT. In the dog model, we propose to correlate renal clearance measurements with DTPA curve parameters pre-and post-RAS and develop a means of separating glomerular filtration of DTPA from curve parameters representing changes in flow. In man, we plan to evaluate the DTPA renal flow study with and without CEI in normal volunteers as well as in patients with essential and RVHT. Patients with RVHT will also be serially re-evaluated to follow the response to medical therapy and to assess changes following surgical intervention or angioplasty. Improved detectiona nd serial assessment of kidney perfusion and function in RVHT by these techniques could result in a cost effective means of improving the diagnosis of a significant segment of the hypertensive population.